1. Field of the Invention
The present invention relates to a power supply apparatus in an information processing system, particularly, it relates to the structure of a back-up power unit provided in a power supply apparatus.
2. Description of the Related Art
In general, a power supply apparatus used for an information processing system is formed by a plurality of power units each connected in parallel to a commercial AC (alternating current) power source, and each power unit includes a back-up battery. To connect power units in parallel and to provide the back-up battery give high reliability to the system when a failure accidentally occurs in the system.
For example, if a failure occurs in an active power unit, the power is immediately switched to another stand-by power unit. Further, if a failure occurs in the commercial AC power source, the power is immediately switched to the back-up battery.
On the other hand, there is a very important problem in the above power supply apparatus formed by a plurality of power units and a back-up battery. This is, how to prevent a current leakage flowing from the active power unit to another stand-by power unit through the back-up battery. In this case, how many batteries can be provided and where the battery should be located in the power supply apparatus, are very important questions since the answers influence the current leakage as explained in detail below.